Many mineral processing plants and techniques for metal production are sensitive to the mineralogical content as well as the elemental composition of the feedstock fed into the processing plant. In many cases, the mineralogical composition rather than the chemical composition of a process stream is the most important factor in terms of plant performance in mineral processing.
Direct mineralogical analysis of process streams is mainly limited to off-line techniques. Widely used techniques include scanning electron microscopy [Sutherland 1991]1 and conventional X-ray diffraction (XRD) [Roach 1998]2. These techniques require removal of a small sample, or assay, from the process stream which is taken to a laboratory for analysis. However, the small quantity of sample normally extracted for such assays, from the immense volumes usually encountered in a processing plant, is generally not well related to the information needed for accurate control which leads to large sampling errors. In addition, the lag time before the analysis is available can result in substantial cost. Subsequently, off-line analysis is considered ill suited to process control, especially for slurries, which demands regular and rapid analysis of the process stream.
Conventional XRD is based on angle-dispersive techniques which tend to require expensive equipment. An alternative technique is the energy dispersive technique EDXRD which is based on polychromatic radiation. The interference of the lattice planes reflections corresponding to the Bragg-equation is investigated by the diffraction intensity of the different wavelengths rather than varying the Bragg-angle as in conventional XRD.
On-line monitoring of process streams, on the other hand, is primarily restricted to elemental analysers, which measure the chemical composition of the material in the process stream. Widely used on-line elemental analysis techniques for process monitoring and control include X-ray fluorescence (XRF) [Smallbone 1977]3 and prompt neutron/gamma-ray activation analysis (PGNAA) [Sowerby 2005]4. The mineralogical content of the stream is determined using prior knowledge of the relationship between the chemical and mineralogical composition of the material in question. However such techniques are unable to distinguish between minerals (for example anatase and rutile) having the same chemical composition (in this case TiO2). Furthermore the presence of the same element in a number of different materials making up a process stream can result in misleading results. For example if the quantity of quartz (SiO2) needs to be known, the results will be affected by the presence of Si and O in other materials contained in the process stream.
A quasi on-line mineralogical analyser using conventional angular dispersive X-ray diffraction has been proposed [Scarlett 2001]5. However this technique requires complex automated sample handling equipment and has had only limited application.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.